Description (as provided by applicant): Polycystic kidney disease (PKD) is characterized by the formation of innumerous fluid-filled cysts that can expand to several centimeters in diameter due to aberrant cell proliferation. The insistent enlargement of cysts disrupts the normal renal architecture, leading to progressive loss of renal function. cAMP agonists, including arginine vasopressin, stimulate the mitogen-activated protein kinase (MAPK) ERK and accelerate the proliferation of cyst-lining epithelial cells. B-Raf, a MAPK kinase kinase appears to be an important intermediate in cAMP-dependent proliferation of PKD cells. cAMP increases B-Raf activity leading to stimulation of MEK/ERK signaling and cell proliferation. In preliminary experiments, we found that Raf inhibition with Sorafenib (Bay 43-9006) decreased cAMP-induced ERK activity and PKD cell proliferation. In contrast to PKD cells, in normal tubule cells, B-Raf is repressed and cAMP does not stimulate ERK and cell proliferation. Thus, in vitro evidence suggests that B-Raf is a potential therapeutic target for slowing cyst growth in PKD. To determine if B-Raf activation is sufficient to induce the formation of renal cysts and development of PKD, we generated transgenic mice that express constructs driven by a CMV promoter that contain a floxed-lacZ-polyadenylation-stop sequence placed in front of wild type B-Raf or BRAF(V600E), the most common B-Raf activating mutation. These transgenic mice will be crossed with Ksp-Cre mice, which express kidney specific Cre recombinase, to selectively overexpress wild type B-Raf or BRAF(V600E) in the collecting ducts. The long term goal of this project is to determine if kidney-specific expression of active B-Raf induces renal cyst and/or tumor formation, de novo, and/or accelerates the rate of cyst growth in mice with genetic forms of PKD. We will use Competitive Revision funds from the ARRA stimulus to hire a new full-time Research Assistant for 12 months, purchase research supplies, and pay animal costs. Completion of these studies will provide important "proof of concept" evidence that B-Raf is a central intermediate for aberrant tubule epithelial cell proliferation involved in cyst expansion and will provide a strong rationale for the development of small molecule drugs that target B-Raf in human PKD. RELEVANCE: The requested supplemental funds will help stimulate the local and United States economy as they will provide short-term expenditures for new laboratory personnel, provide funds to purchase research supplies and provide funding for animal care, including veterinary and animal husbandry staff.